Sulphuric acid



Oct. 11, 1932.

AIR

BURNER,

c. B. CLARK 1,882,208

SULPHURIC "AC ID Filed July 9, 1929 SURPLUS ACID 1 J K TO STORAqE ACIDTO F TOWER *1 CONDENSED C 8 A FROM COLL EC'TOR- G BZ T WEK H FR 0 DUST COLLECT? SCRUBBER COLLECTOR F WATER FOR, cooum COLLECTOR M IST COLLECTOR,

CONDENSED ACID TO &

qns TO PROCESS avwemtoz Cram .5. GLfi/BK Patented Oct. 11, 1932 CYBIL B. CLARK, OF SCARSIDALE, N EW YORK, ASSIGNOR TO CATALYTIC PROCESS coin d RATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE SULPHURIG ACID Application fi led July 9, 1929. Serial No. 376,930.

My invention relates more particularly to improved methods for the production of sulphuric acid and sulphur trioXide by the contact sulphuric acid process in which the catalyst employed is not poisoned by the ordinary gaseous poisons, such as arsenic, hydrochloric acid, chlorine, selenium etc. arising from burning or roasting a sulphur containing material as pyrite to produce sulphur dioxide. As an example of the type of catalyst preferably used in my methods, I refer to the forms of vanadium catalysts described in the two U. S. patents to J aeger No. 1,675,- 308 of June 26, 1928 and No. 1,694,123 of December 4, 1928. Y

en using platinum or other catalysts that are poisoned and rendered inactive by gaseous impurities, it is necessary to remove from the burner gases not only the solid particles but also any liquid particles and gaseous poisons if such-are present. When an arsenical iron sulphide ore is used as a raw material, such a plant will use for purifying the gas the following equipment: dust collectors, scrubbers, coolers and mist removers. To remove gaseous impurities such as arsenic the gas should be cooled to about atmospheric temperature and then the cooled gas is washed with water, weak acid or alkaline solutions.

The use of vanadium catalysts eliminates several of the disadvantages, such as scrubbing with water, weak acid or alkaline solutions which necessarily introduces a large amount of water into the.

gas with the disadvantageous result that the gas is saturated with water vapor as it leaves the purification system. Such undesired moisture should be removed by drying the gas with sulphuric acid before entering the converter to prevent condensation of acid and corrosion of equipment beyond the converters. During warm humid weather the amount of water entering the drying system is often so great as to restrict to a large extent the amount of strong sulphuric acid or oleum produced.

A further objection is that the heated gas from the burners cannot be handled in iron equipment below the condensation point of sulphuric acid due to corrosion from the weak acid that will be condensed from the gas. A still furtherobjection to the present purification system lies in the fluctuating amount of water introduced varying from 0.20 of a pound or less of watervapor per 1000 cubic feetof gas in winter to 1.7 5 pounds or more in summer. Such water combines with the S0 formed in the burners and gives a condensed acid in the purification equip and simplified and vapor carried by the thereby exerting an exact and predetermined control of the strength of the acid condensed in therpurification system. This feature is a distinct advantage in that strong acid can be produced of a definite strength which will permit the use of iron equipment, throughout the purification system.

Again the strength of the condensed acid in the improved purification system is so regulated that such strength has a low aquein a dry condition thereby avoiding further drying before the gas passes to the con- Verters. 7

Of the drawing, illustration of the various major steps of the process are carried out through the converter, cooler and absorber;

Fig. 1 is a diagrammatic ous vapor pressure which maintainsthe gas apparatus in which the Fig. 2 is a similar lay-out of the first steps of the process, showing an alternative method of cooling the gas and condensing the acid when a relatively small amount of dust and fume remains in the gas following the dust collector. v

same parts in both figures.

. Referring to Fig. 1, part of the air enters "the drying tower A by suction. from the blower B, the tower A containing strong sulphuric :acid 'by which the air'entering the tower A is dried. Between the drying tower A and the ore burner G a controlled amount of- -undried or atmospheric air isintroduced into the system through the flue comiectionv burner Cis sofre'gulat'ed thatan'acid of about D in which is located tliecontrol valve or damper E. According'to my lmproyed pro cedure the ratio of dried to undried or atmospheric air is varied togiveia definite amountof moisture entering the burner C,

and varies according to atmospheric conditions,'the amount of sulphur trioxide produced in the burner annuals; strength ofthe acid to becondensed out of the purification system.

Changes in of S0 formed inthe burner C, or the temperature to which the gases are cooled, all of which might change the strength ofthe condensed acid can" readily be provided for of dried to undried air by shifting the damper flueD. This is due to entering the burner G E in the undried air the fact that with a constant amount of moisture entering the burner G coupled with a "constant formation of, S0 therein, a con- 7 stant strength-of acid can be condensed in 1 ltion 1n strong sulphuric acid. Water or weak n r acid is added totheabsorber N in amount the dust'collector B where most of the dust .present in the gas is removed. Such.

the purification equipment.

After leaving theburner Othe as 1 z: 1 however, may still contaln some fine-c dust and various impurities such as arsenic, lead or zinc compounds inthe form 'of fine fume,

or in such a state that they will condense as the gas is cooled; The gas then passes through thescrubber G and mist collector H. 1

In thisFig. 1 apparatus theacidcondensed in the scrubber G and mist collector H is circulated over the scrubber G and the amount of acid withdrawnfrom the system is-substantially equal in amount to the acid condensed. The hotacid from the scrubber 'G is cooled in the acid cooler I and the solid impurities removed by settling before the acid is returned throughthe' pump J to the scrubber G. Through pipeK from the cooler I all surplus acid is withdrawn to storage. By varying the amount ofacid circulated and its cooling in the cooler I the. .temperature of the gas and removal of dust and fume therefrom can be regulated to suit 7 the requirements;

, I havediscovered that; when a relatively large amountof dust and fume 'is present in the gasunder ordinary operating-conditions, a considerableamount of such fume will pass the scrubber G which is difiicu'lt toremove from the gas unless special .con-

trolled conditions exist.

suficiently to require no further iT'ijig through the'blower Bito the converter L.

P I V 'throughthe system by suction,but thereafter humidity of the air, the amount perature for starting conversion.

7 particles removal as hereinbefore described. The con-- densed acid is removed from the cooling tubes I have found thatwith acid of strength of about 92% only part of the sulphur trioxide Preferably the drying of theair entering the 92% strength will be condensed in scrubber G and mist collector II and a temperature of about 167-? F:

The gas leaving-the mist collector H is now ry and free from lmpuritles as treatment before passto the blower thegas has been drawn the gas is forced by pressurethroughthe converter Land through the rest of the system. This converter L may be of the Seldentype in which the heat generated in the converter is used to preheat the gas to a suitable tem- Any other type of converter system may be used if desired. In the Selden converter the gas will pass at'about 7 50 F.1to the cooler M which may be ofanywell-known type. The cooled S0 gas then passes to the absorber N where the sulphur trioxide is removed by absorpsufiici-ent to form the desired strength of acid Referring to Fig. 2, I have shown an alternative method of cooling the gas and condensing the acid when a relatively small amount of dust and fume remains in the gas following the dust collector F. In this method shown in Fig. v2 the scrubber G may be dispensed withand the iron tubes 0 cooled by water sprays P may be substituted. The gas passes through tubesO and is there cooled out of contact with water under such conditions that the: acid will-condense on the dust and fume assisting in their condensation and O and mist collector H to storage while the dry gas leaves the collector H to the converter L asinFigcl. I

Byeither method of cooling an acid of about 92% strength will be condensed ifthe gas iscooled to about 167 F., and the gas is practically dry as it is sucked out of the mist collecter The strength of the acid may be tested acid is stronger-than 92%, the damper E can strength-*isbelow 92% this damper can be in any suitable way. If the condensed be opened 'to allow moreundried air to enter I the system through the flue F; if the acid partly closed; i Such shifting of the damper E provides an easy method of control for the strength of the acid condensed out of the system before conversio An example of the operation of my improved methods is as follows, it being under: stood that such example is merely indicative of certain procedures for carrying out the principles of the invention without being limited to the exact details set forth.

hen using iron pyrites ore of the 5% of the sulphur in the burner C oxidized to sulphur trioxide ($0 the method of operation is substantially as follows If the air used has a relative humidity of at 70 F. I dry in the tower A about 70% of the air used for introduction in the burner C. If the air has a relative humidity of 30% at 70 F., I dry about 28% of the air used. The amount of air so dried in the tower A is regulated by the shifting of the damper E as hereinbefore described.

Under these conditions the amount of moisture entering the burner C will be about 0.277 lbs. per 100 cu. ft. of 7% sulphur dioxide (S0 gas figured to standard conditions. In the burner C 0.837 lbs. of sulphur trioxide (S0 per 1000 cu. ft. of gas will be formed. As the gas cools in the scrubber G or cooling pipes O and mist collector H, the water in the gas will combine with the sulphur trioxide (S0 forming sulphuric acid of about 92% strength if the gas is cooled to about 167 F.

The strength of the acid condensed may be varied by varying the amount of moisture entering the system at the burner C through manipulation of the damper E.

Acid of predetermined strength may be formed in the purification system and iron equipment can be used throughout, while the low aqueous vapor pressure of the condensed acid maintains the gas in a dry condition requiring no further drying before passing into the converter L.

In the foregoing description I have set forth preferred forms of apparatus or equipment and a preferred procedure to be followed in carrying out the invention. However, it is to be understood that the practice of my improved methods is not in any way limited to the use of the particular equipment illustrated or to the procedure described, or to the particular type of catalysts set forth in the J aeger patents mentioned.

claim as my invention 1. In processes for the manufacture of sulphuric acid by the contact process when burning sulphur-containing ores the step which consists in producing oxidation of sulphur with a mixture of partly dried air and atmospheric air.

2. In processes for sulphuric acid by the contact process when burning sulphur-containing ores the step which consists in producing gases by the the manufacture of I oxidation of sulphur with a variably controlled mixture of partly dried air and atmospheric air.

3. In processes for the manufacture of sulphuric acid of predetermined strength in the purification system, the step which consists in injecting controlled amounts of moisture-laden air admixed with previously dried air in the production of the burner gases by the oxidation of sulphur-containing material.

4. In processes for the manufacture of sulphuric acid by the contact process when burning sulphur-containing ores the step which consists in varying the ratio of dried to moisture-laden air in producing gases by the oxidation of sulphur-containing material for subsequent condensation of acid particles on the impurities in the gases.

5. In processes for the manufacture of sulphuric acid by the contact process when burning sulphur-containing ores the step which consists in varying the ratio of dried to moisture-laden air burner gases by the oxidation of sulphurcontaining material to obtain upon condensation an acid of low aqueous vapor pressure.

6. In processes for the manufacture of sulphuric acid by the contact process when burning sulphur-containing ores and using a vanadium catalyst, the steps which consist in producing gases by the oxidation of sulphur-containing material with a variably controlled ratio of dried and moisture-laden air, cooling the gas mixture to condense the acid therein, and thereafter passing the dried gases to a converter containing said catalyst.

GYRIL B. CLARK.

gases by the I in producing the hot 7 

